hard shifts will not get 4th 89 Firebird
 

89 Firebird, 305, throttle body, 700R4.. Trans runs up to approx 2800 to shift from first to second and second to third. Shifts are hard. Will not shift to 4th. Torque Conv does not lock up. At any speed, let off on gas and tach drops to 500 rpm and car freewheels. Fluid is not low and trans shifted just fine, until it didn't. Can anybody give me a clue as to where to start? Thanks. Bob